A Study to Compare the Results of FGFR Testing by Either ctDNA Blood Testing or Standard Tumor Tissue Testing

Recently, the first targeted therapy for patients with metastatic urothelial cancer (mUC) received approval, i.e. erdafitinib. Erdafitinib is a pan-FGFR small molecule inhibitor. Approximately twenty percent of mUC patients' tumors harbor qualifying alterations in FGFR2 or FGFR3. Currently, standard testing uses archival tumor tissue. However, this type of testing may not be representative of a patient's clinically dominant tumor clone at the time of treatment initiation due to temporal and spatial biopsy bias of archival tissue testing.

In this study, patients will undergo circulating tumor DNA testing, in addition to conventional tissue testing, for treatment eligibility. Investigators hypothesize that blood-based ctDNA testing will provide a more accurate assessment of somatic FGFR status than same patient archival primary tissue.

This study's objectives are:

Objective 1 (Primary): To evaluate the diagnostic value of ctDNA testing against the "gold standard" of tissue testing.

Objective 2 (Secondary): To evaluate whether ctDNA may be a superior predictive marker by identifying actionable FGFR alterations that are currently missed on tissue assays.

Procedures:

• Medical history will be reviewed, including all previous anti-cancer treatments.

• A blood sample will be collected for ctDNA testing at the time of screening for FGFR alterations and at progression under erdafitinib therapy. Test results will be compared to archival tissue testing.